This invention relates generally to devices for the treatment of bone fractures, and, more particularly, to a pin clamping device particularly adapted for use in an external fixation device for positioning and immobilizing the distal segment and the proximal segment of a fractured bone to apply controlled distraction and compression to the fracture.
External skeleton fixation devices have been developed in recent years for the treatment of long bone fractures with substantial soft tissue involvement as an alternative to prior art internal fixation devices such as bone plates, and to replace prior art treatment methods such as immobilization of the affected limb using traction devices. External fixation devices generally comprise one or more pins secured to the distal segment and to the proximal segment of a fractured bone, which are adjustably connected by pin clamps to a frame located externally of the affected limb. Each pin has a threaded portion inserted into the cortical bone of the proximal or distal bone segment, and a smooth, clamping portion located exteriorly of the limb. Once the bone segments are aligned in the correct anatomical position with the pins in place, the clamping portion of the pins are secured to the frame of the external fixation device by the pin clamps to maintain the bone segments in position.
Prior art pin clamps for use in external fixation devices generally comprise a pair of clamping blocks having facing surfaces each formed with a number of spaced notches. The clamping blocks are secured together by screws or other fasteners so that the notches in their facing surfaces align to form annular passageways which receive and grip the clamping portion of the pins.
Prior art pin clamps of the type described above have several limitations. One limitation is that the normal force applied to the pins by the mating clamping blocks is dependent solely upon the force with which the screws mounting the clamping blocks together are tightened. If the screws are tightened too loosely, the pins can work free within the clamping blocks and allow the bone segments which they support to move out of position within the limb. In addition, many prior art clamping blocks engage only a relatively small portion of the length of the pins which further limits the gripping force applied to the pins.
In reducing a fracture of a long bone, a drill guide having the same number and spacing of passageways as the pin clamp is first placed against the limb so that the surgeon can use the passageways in the drill guide to drill holes in the bone segments. The pins are inserted into the guide holes made in both the proximal segment and the distal segment of the bone, and the drill guide is then removed. Once the pins are in place in the bone, the frame of the external fixation device is then positioned with respect to the limb so that the clamping portions of the pins are received within the pin clamps of the frame and clamped in place. It is often difficult to obtain accurate pin placement in this fashion, particularly where further adjustment of the position of the bone segments, and, in turn, the pins, is required to reduce the fracture after the frame is in place.
Another limitation of prior art pin clamps is that they do not permit manipulation of the pins relative thereto once the pins are received in the passageways of the pin clamps. Since the method of inserting pins into the bone segments described above may not result in precise pin placement, some adjustment of the pins relative to the pin clamps may be necessary in the event of misalignment, particularly if further reduction of the fracture is necessary after the frame is in place.
Additionally, even if the pins are properly aligned with the passageways of the pin clamps when the frame is in position, many surgeons prefer to manipulate the clamping end of the pins so that the threaded portion in the bone becomes wedged within the pre-drilled bores. This manipulation of the pins applies a force between the pins and bone, and, in addition to the threads of the pins, helps hold the pins in place in the bone. The annular passageways of prior art pin clamps do not permit such adjustment, which could result in loosening of the pins within the bone.